Mast stabilizer for lift trucks

ABSTRACT

Means for stabilizing the mast of a lift truck so that load sway is reduced and loads can be elevated to greater heights for loading into storage racks. Movement of the mast in a horizontal direction is arrested by a carriage which travels on vertical tracks as the lift truck mast is elevated.

United States Patent 1191 Dickenson, deceased MAST STABILIZER FOR LIFI TRUCKS Richard W. Dickenson, deceased, late of Pickerington, Ohio by Winifred Dickenson, executrix Inventor:

Assignee: Anchor Hocking Corporation,

Lancaster, Ohio Filed: Apr. 12, 1972 Appl. No.: 243,249

US. Cl 187/9, 187/95, 182/229, 214/16.4 A, 212/39 A Int. Cl B66b 9/20, B66b 7/02 Field of Search 187/9, 95; 182/229; 2l4/l6.4 A; 212/39 A References Cited UNITED STATES PATENTS 10/1972 Weisker et al 2l4/l6.4 A

[ Dec. 25, 1973 3,487,893 Ryskamp 187/95 x 3,542,161 11/1970 Ulinski 187/9 87,083 2/1869 Tufts..... 187/95 1,554,584 9/1925 Lake..... 187/9 x 2,374,298 4/1945 Nassetl 212 39 A Primary Examiner-Robert S. Ward, Jr. Attorney-James S. Hight et al.

[57] ABSTRACT Means for stabilizing the mast of a lift truck so that load sway is reduced and'loads can be elevated to greater heights for loading into storage racks. Movement of the mast in a horizontal direction is arrested by a carriage which travels on vertical tracks as the lift truck mast is elevated.

16 Claims, 5 Drawing Figures PAIENTEUUEEZSBYS SNEU 2 [If 3 1 MAST STABILIZER FOR LIFT TRUCKS This invention relates to trucks with elevatable lifts, of the type used for carrying loads to and from vertically spaced racks, and moving loads up to and down from the racks. In particular, the invention is directed to means for stabilizing the elevatable mast which carries the lift and the load, so that the mast cannot tip out of vertical position even when extended to extreme lift heights.

Lift trucks, especially fork lifts, are used at warehousing and other facilities both to transport loads over the ground, and to move them vertically for placing or removing them at elevated positions on racks or shelves. Such trucks include a mast which is an upstanding boom or support structure along which the generally horizontal platform or lift can be raised. The mast is often of a telescoping nature, so that it can be extended to heights several times its retracted height.

At the present time, lift trucks are limited to vertical lifts of approximately twenty feet, at least where loads of roughly about 1,000 pounds or more are being handled. Beyond this approximate upper lift limit of 20 feet, loads tend to become increasingly unstable, difficult to manage, and dangerous.

In theory, if a load is raised along a vertical path, its height above the lift truck should not affect its relative stability, or present any increasing danger, so long as it is under control. However, in practice lift masts are not always in a truly vertical attitude. Usually the mast inclination (in a vertical plane extending longitudinally through the truck) is adjustable, so that the mast can be canted forward to pick up a load, and back to hold it while the truck is moving over the ground. If the mast is inadvertently canted slightly forward of the vertical, or if the floor is not level, then the load will not move along a vertical line whenit is elevated. When a load is elevated by a mast which is forwardly inclined, the horizontal spacing increases between the load and the truck front wheels which act as a fulcrum. The load, acting through this lever arm, comes increasingly closer as it is raised, to a point at which tipping can occur. Depending on mast angulation, load height and weight, tipping can and sometimes does occur and it presents a likelihood of real danger to the operator, truck and load. The danger is still greater if the truck is one which has a scissors lift mount, by which the lift can purposely be shifted forward with the load on it, because scissors extension directly changes the lever arm, and, hence, the danger. Apart from the danger of mast misalignment, even sway while the load is being jockied into position at an elevated rack may tend to create mast instability. And even if the mast is perfectly vertical with respect to the truck, sidewise tilt of the truck can present a potentially dangerous condition. The higher the mast extension, the greater is the danger that an out-of-vertical alignment load will cause the truck to tip over.

These factors have imposed a practical upper limit on mast extension for day in, day out operation, even though greater extensions are technically feasible. Even below that limit, lift truck manufacturers suggest lighter load capacities with increasing mast extension. For example, one manufacturer recommends that for a particular truck, the capacity should be diminished from 4700 pounds at 144 inches (12 feet), down to 2,900 pounds at 216 inches (18 feet)a reduction of about 40 percent.

This practical limit of mast extension is becoming an important determinant of warehous height and, hence, the total volume of material that can be stored on a given floor area. The possibility of being able to load racks at heights of more than 20 feet would directly increase the storage capacity of a given floor area. At present, however, the practical lift limits on truck operation deter construction of warehouse racks more than 20 feet above the floor.

In place of lift trucks, some storage facilities use travelling elevators that are suspended from overhead rails, or that are guided between fixed upper and lower rails. By reason of the stabilization that the overhead guides provide, the elevator systems are not as critically limited as the trucks in regard to maximum lift height, but their cost is substantially greater and they are not as flexible in use as lift trucks because they are confined to predetermined paths of travel along fixed rails, whereas a lift truck is steerable over any route selected.

This invention is directed to stabilizing means for use with a lift truck which will enable the truck to be used with a high degree of safety to elevate a full load to heights substantially exceeding the present lift limit. Useful rack heights can therefore be increased without the necessity of restoring to -fixed path travelling elevator systems.

The invention contemplates a vertical guide means mounted adjacent each vertical column of racks which the truck is to serve, a carriage which is vertically slidable along the guide means between lowered and raised positions, and means for disengageably engaging the mast of the lift truck with the guide means through the carriage. When engaged, the guide means permits the mast to move only in the vertical direction; it prevents any horizontal component of movement of the mast with respect to the rack and guide means, and thereby stabilizes the mast, load and truck against tipping or swaying.

It is an important advantage of the invention that the mast is rapidly disengageable from the guide means, so that it is not confined to movement along a predetermined horizontal path. The stabilizing means controls the mast movement only when the truck is coupled to the guide means at a particular column of racks.

The vertical guide means may be of various specific embodiments, to perform the carriage guiding function. In broad terms, the guide means comprises two vertical rails or tracks, one adjacent each vertical side of the column of racks. The carriage moves along these rails or tracks, so that it travels along a fixed vertical path.

The guide means are preferably in the form of U- shaped channels or l-beams, mounted to a part of the rack support structure itself. The guide means should extend the full vertical distance over which mast stabilization is necessary, and they should be spaced at the sides of the rack, so that the access space directly in front of the racks is unobstructed for the loading operation.

The carriage which is guided by the guide means preferably includes rollers, sleeves or sliding shoes engageable with the guide means, for example, running in a U-shaped channel such that the carriage can move up and down vertically, but not pivotally or in the horizontal direction. The carriage can be mounted to the mast of the lift truck for movement with the lift truck from location to location for quick connection to the guide means at a given location at which the load is to be elevated. Alternatively, however, each vertical column of racks may have its own carriage, to which the truck mast is disconnectably connected as by a post and socket fitting, and which remains at the racks when the truck is absent. The latter arrangement is generally more expensive than the former in that a carriage installation must be provided for each column of racks, but it permits more rapid interconnection of the mast to the guide means.

Actual use of the stabilizing means at a given rack position by coupling the mast to the guide means at that station, may be optional. Where the load is to be moved only a small vertical distance, stabilizing is not needed and the lift may be elevated without connecting the mast to the guide means. To facilitate this option the carriage may have a lower limit of travel on the guide means such that it remains above, and hence out of the way of the mast, for low level loading operations. When the mast is to be elevated above a certain height, for exampl vq j f t a which ,r l daqasrsyslqe instability might arise, the mast is then interconnected? to the guide means through the carriage. The connection is made at the lower limit of carriage travel, and the mast is thereafter elevated in stabilized engagement with the carriage.

To make the connection to the guide means, the mast is positioned vertically. Where the carriage: remains oermanently attached to the guide means, the interconnection of the mast to it can be made simply by elevating the mast to seat a post or pin into a socket, so that the mast cannot thereafter move laterally with respect to the carriage.

If the carriage is mounted on the mast for travel with the truck, it is connected to the guide means by a latch or other releasable connector.

Once the mast is coupled to the guide means, the carriage and mast can move vertically only. Tipping, swaying or other movement out of vertical condition is prevented. With the carriage attachment, safety becomes a much less limiting factor on mast heights, and, hence, on warehouse heights.

In order to facilitate proper positioning of the truck at a given position for coupling to the vertical guide means, it is desirable to provide a stop in front of the rack such that when the front wheels of the truck are positioned against the stop, the mast will be so located that, when extended, it will properly engage the carriage or rails.

A mast angulation indicator or inclinometer, which may be a bubble level, a bob, or other angulation showing device, is disclosed as a useful adjunct to align the mast in proper vertical condition before elevation is started.

Those skilled in the art will appreciate that as a mast is elevated toward a height of about 20 feet, it becomes increasingly difficult, from the truck operators position, to accurately judge the height of the load in relation to the rack. The relative positions of the rack and the load are difficult for the operator to preceive. The lift might be somewhat beneath the rack shelf so that the load would bump into the shelf when moved toward it for loading. For that reason, the invention also provides means for showing the height of a load in relation to shelf or rack height, as a desirable addition.

The invention can best be further described by'reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a series of columns of racks in a warehouse, each column being equipped with one form of stabilizing means in accordance with the invention, the figure showing a fork lift engaged with the carriage of one rack column and the load raised to an upper tier or shelf;

FIG. 2 is a perspective detail, partly broken away, of a carriage in accordance with one embodiment wherein the carriage is captured rollably between guide means in the form of I-beams and the truck is disengageable from the carriage;

FIG. 3 is a fragmentary perspective view of a simplified alternative embodiment of the invention wherein vertical cables comprise the guide means;

FIG. 4 is a fragmentary perspective view of a third embodiment whereby a carriage attached to the truck is releasably connectable to guide beams at a rack; and

FIG. 5 is a vertical section showing the details of the releasable connection of the truck mounted carriage of FIG. 4.

The warehouse rack designated generally at 10 in FIG. 1 comprises a rectangular framework having a series of spaced vertical support members 11 and spaced horizontal support members 12. Taken together, each pair of adjacent vertical supports 11 and horizontal supports 12 defines a compartment, shelf or bin 13 which is referred to herein as a storage space. Each space 13 includes means for receiving and supporting a load placed in it by the truck. Taken together the storage spaces which are between each adjacent pair of vertical supports 11 comprise what is referred to herein as a column 15 of racks.

Insofar as described thus far, the rack may be of conventional construction, except that its height will advantageously exceed the usual height to which racks have been limited by reason of the previously mentioned upper limit of mast elevation for lift trucks.

Each vertical support 11 includes vertical guide means. In this embodiment, the guide means are tracks formed by I-beams. As shown in detail in FIG. 2, each beam has an outer flange l7 and an inner flange 18, the two flanges being connected by a web 19. Together, the respective flanges l7 and 18 and web 19 define a channel 20 between them. The beams 11 are arranged with the flanges l7 and 18 parallel to the front of the rack, so that the channels 20 of adjacent beams open toward one another. These vertical guide means may be an integral part of the track structure itself, or they may be added to existing rack structure to adapt it to the invention.

A carriage is translatable vertically along the guide means, to stabilize the movement of a truck mast. The carriage may take a number of forms. FIGS. 1 and 2 show a carriage 25 of generally triangular structure. This carriage has an angulated frame member 26 at each side, the two members 26 being cross-connected by a post of bar 27 between their outer tips. At its ends each frame member 26 is provided with an interconnnection to the guide means which couples the carriage to the latter. This interconnection may be in the form of a pair of spaced rollers 28 and 29 which project from each frame member 26 parallel to the beam flanges and rollable about horizontal axes. The rollers 28 and 29 of each pair of the four pairs of rollers on carriage 25 are spaced apart from one another on the leg of frame member 26 so that they engage opposite sides of the respective outer flange 17 or 18. The carriage 25 is thereby confined and guided for movement in a vertical direction. The rollers provide free movability of the carriage in the vertical direction with a minimum of binding or sticking on the tracks, but resist movement in the horizontal plane by reason of the engagement of the opposed frame members 26, 26 with the flanges 17 or 18. The rollers 28 which are captured within the channels may be removable from the frame members 26 for connection or removal of the carriage at a particular rack column.

The bar or cross beam 27 of carriage is disconnectably engageable with the elevatable mast 30 of a lift truck 31. Apparat from the provision on the truck of the stabilizing structure of the invention, the truck 31 may be entirely conventional. As shown in FIG. 1, the truck mast 30 includes a number of telescoping sections, each designated at 35, which can be elevated, as by a chain or telescoping piston, to raise a fork or other type of lift 32. The top height or mast extension may conveniently be in the range of 20-35 feet.

In the embodiment illustrated, the fork 32 is equipped with a scissors" or extender 33 whereby the fork can be moved forwardly from the mast in the horizontal direction, to move a load into or out of the compartment. The scissors may be conventional.

The mast includes coupling means for interconnection with the carriage 25. The top mast section is provided with a forwardly projecting top member 38 that has an upstanding located centrally post 39. Post 39 is positioned to interengage and seat in a cooperating downwardly opening socket 40 in carriage cross beam 27, when properly aligned with it. Specifically, when the truck is positioned so that post 39 is directly beneath socket 40 and the mast is elevated, post 39 will automatically engage in the socket 40. The socket may have tapered sidewalls to center the stud properly. When the post has been brought into the socket by upward movement of the mast, the carriage will thereafter move upwardly by and with the mast. Gravity will cause the carriage to follow downward movement of the mast of the latter. It is noted that the positions of the post and socket can be reversed, that is, the post could project downwardly from the beam 27, with the socket in mast top bar 38.

A stop 44 is mounted on either or both of the vertical supports 11, 11 at each column 15 of racks. These stops 44 limit the downward range of travel of the carriages, so that the inactive carriages are stopped at positions just above the lowered position of the truck mast (see FIG. 1 When the truck is positioned properly be fore a particular column and the mast is raised, it then engages the carriage and, through the carriage, the guide means.

From the foregoing it can be seen that the truck must be in a predetermined position of alignment in front of a given rack column 15, so that when the mast is elevated the coupling means will move along a path of travel that will cause it to couple with the carriage. For example, if the mast is not vertically aligned, extension of the mast will tend to move the post either closer to or farther from the rack (in the horizontal direction), and could cause jamming.

For this purpose, it is desirable to provide truck positioning means that will enable the operator easily and quickly to stop the truck in proper alignment before the respective rack column 15. Such means comprise a floor groove, channel or stop such as that designated at 45 in FIG. 1 which engages and stops the truck front wheels when the post 39 is directly beneath the socket 40. the truck can be centered laterally in front of the rack column by a center line; alternatively, the channel 45 may have end guides positioned for this purpose.

In order to insure mast verticality, it is desirable to provide a bubble level, bob or counterweight mounted to the mast to show its angulation with respect to vertical. A preferred form of the mast angulation indicator is shown in FIG. 1. This includes an indicator arm 47 attached to the mast for pivoting movement with it. The arm reads on a dial 48 on the truck body. It can be seen that when the mast is inclined forwardly, the arm 47 will move out of centered or vertical position shown in FIG. 1, according to its angulation.

From the working position of the operator (as shown in FIG. 1) it may be difficult for him to judge correctly the elevation of the fork 36 and load 14 on it with respect to a given compartment 13 into which the load is to be placed. For that reason, it is further desirable to provide a mast elevation indicator that shows the mast extension. Preferably this correlates the mast position directly to compartment position. A preferred form of elevation indicator for this purpose is shown in FIG. 2. A coiled steel tape or band 55 is mounted to a vertical support 13, below stop 44. This band is of the flexible rule type, and has a spring rewind. Movement of the tape is coupled through reduction gearing to read out on an indicator dial 56. One end of the tape 55 is connected to the carriage, as at 57, so as to move with the carriage as the latter travels up or down. The dial 56 is calibrated to show lift position in relation to compartment number; in FIG. 2, the dial is shown as indicating that the lift is in position for loading compartment 10 (i.e., the 10th compartment as numbered from the floor). This corresponds to the mast position shown in FIG. 1. Thus, by observing indicator 56 at eye level, the operator can tell accurately when the scissors can be extended to slide the load smoothly into the compartment.

As the scissors are operated to move the load forward and into the compartment, this increases the horizontal lever arm of the load with respect to the front wheels 58 of the truck, which act as a fulcrum. However, the engagement of post 39 in carriage socket 40 will prevent the mast, and hence the truck from tilting forwardly, sideways, rearwardly, and in fact from moving significantly in any direction except the vertical direction.

FIG. 2 also shows a compartment roller system which is a desirable but not a necessary adjunct to the stabilizing means. This roller system facilitates loading and removal of a load from a given compartment. The horizontal supports l2, 12 of each compartment are provided with free rollers 60, for supporting a load at its edges. Each compartment also includes two endless chain loops, one of which is shown at 61 in FIG. 2, and each is mounted to the supports 12 and running over end sprockets as at 64. Pusher bars 62 are mounted between the two loops 61 at spaced intervals. The pushers present upstanding rails which will engage the forward or leading edge of a load when the load is pushed forwardly over the rollers 60. The load will thus bump into a pusher bar 62, moving the pushers and the loops 61 into the compartment with it. Loads ahead of it in the compartment will be pushed further into the compartment.

When a load is to be removed from the compartment, the lift is brought to bear against a pusher such as that at 63 which is on the downside of the chain loop, to push it forward, i.e., into the compartment. The resulting movement of the loop carries the pushers on the up side to move the load out of the bin and onto the fork for removal. The rollers may be slightly inclined, suitably at about 3, to assist in carrying loads with the bin.

A simplified type of carriage and vertical guide means is shown in FIG. 3 of the drawings. in this embodiment the vertical guide means comprise two taut wire or bar cables 65 and 66, mounted in front of and adjacent to the respective vertical supports of a column of racks. Tension on the cables is maintained by turnbuckles, not shown. A carriage in the form of a cross member 67 is mounted to and between the cables 65 and 66, by means of sleeves or collars 68, 69 at its respective ends. As in the embodiment first described, the vertical guide means confine the carriage or cross member 67 to vertical movement.

The carriage is connectable to coupling means 70- projecting forwardly from the top of the lift truck mast (in a manner similar to that shown in FIG. 1 by means of a post 71 on the coupling means and a socket 72 on the carriage or cross member 67. A flexible rule 55 is connected to the cross member 67, to provide a read ing of mast elevation.

In the embodiments of FIGS. 1, 2 and 3, the carriage was a part of the installation at each rack, and was disconnectable from the truck mast. As previously indicated, is is also contemplated that the carriage may be mounted to the truck to'move with it, being disconnectably connected to the guide means at each station. This relation offers the advantage that only one carriage need be provided, rather than a carriage at each column of racks. FIGS. 4 and 5 show means whereby a carriage connected to the mast may be removably connected to vertical guide means. In this embodiment the guide means comprise spaced l-beams 75 and 76, mounted adjacent the front of a column of racks. Each beam has two flanges 78 and 79. The outer flange 78 of each beam is notched or cut away as at 77. These notches are of sufficient width and depth to permit a roller 80 on a carriage member 81 to be moved through the notch 77, into the channel 82 that is defined between the flanges 78 and 79 of the respective beam.

The carriage 81 is mounted rigidly to and projects from the truck mast in a manner similar to the top member 38 shown in FIG. 2. At each side the carriage mounts two rollers, the roller 80 previously referred to, and a second roller 83 (see FIGS. 4 and 5). Roller 80 is mounted below and forwardly of roller 83 in relative position such that when theroller 80 is moved through the notch 77 by forward movement of the truck, roller 83 will abut the outerflange 78 of the beam, above notch 77. When carriage 8 1 is moved upwardly from the position shown in FIG. 5, roller 80 will be trapped in the channel 82 of the respective beam, and roller 83 will ride on the outer flange surface. By reason of their spacing, the rollers 80 and 83 prevent movement of the carriage except in a vertical path along the beam. Sidewise or tipping movement of the carriage 81 with respect to the vertical guide means is blocked by one or the other sides of the carriage. It should be noted that the vertical position indicator and the mast angulation indicator are desirable adjuncts to this embodiment of the invention, as well as to the embodiments first described. By these means, the truck can quickly be positioned in front of the tracks 75, 76, moved forward slowly with the carriage at a proper elevation such that the rollers are aligned to pass through the notches 77, and the mast raised so that the carriage is connected between the mast and the beams, and will thereafter stabilize vertical movement of the mast for load transfer.

Having described the invention, what is claimed is:

l. A system for stabilizing the mast of a lift truck as the latter is moving a load vertically at a storage rack, comprising,

fixed vertical guide means presented at a storage rack and extending vertically the distance over which mast stabilization is to be provided,

a carriage which is translatable vertically along said guide means,

an interconnection for coupling said carriage to said guide means for vertical travel with respect thereto, the interconnection of the carriage to the guide means confining the carriage to movement along a vertical path on the guide means and preventing movement of the carriage in a horizontal direction with respect to the said guide means, coupling means on said truck adjacent the top of said mast for connecting said mast to said carriage so that said carriage will be moved vertically along said guide means as said mast is moved vertically while said mast is connected to said carriage, and means for selectively disconnecting said carriage from one of the mast and the vertical guide means so that the truck can move to other racks.

2. The system of claim 1 wherein the vertical guide means comprises two spaced vertical tracks,

and wherein said carriage is mounted to and between said racks for vertical travel thereover.

3. The system of claim 2 wherein the vertical guide means comprise two spaced l-beams mounted at the respective sides of a column of racks.

4. The system of claim 3 wherein the said interconnection includes rollers on said carriage that track on flanges of said l-beams for rolling movement of the carriage with respect to the beams.

5. The system of claim 1 wherein the said coupling means comprises an upstanding post on said mast, and a cooperating downwardly opening socket on said carriage.

6. The system of claim 1 wherein the vertical guide means comprises vertical tracks, said carriage being fixed on said tracks by said interconnection for vertical travel thereover,

and wherein an element projects from the mast and disconnectably interfits with the carriage.

7. The system of claim 1 which further includes stop means for stopping the lift truck at a predetermined position in front of the rack, such that the carriage is in vertical alignment for connection to said one of the mast and the vertical guide means.

8. The system of claim 1 which further includes a stop on the guide means which limits the extent of downward travel of the carriage on the guide means.

9. The system of claim 1 wherein the guide means comprises a pair of vertical cables mounted adjacent the rack,

said carriage comprises a cross member connected between the cables for vertical movement thereover,

and wherein said interconnection comprises sleeves at the respective ends of said cross member slidable over said cables.

10. The system of claim 1 which further includes an elevation indicator providing a readout at ground level of the elevation indicator providing a readout at ground level of the height of the load carried by the lift.

11. The system of claim 10 wherein the elevation indicator comprises aflexible tape connected at one end to the carriage, said indicator including spring rewind means and a dial operated by the rewind means.

12. In combination,

a lift truck having a mast which is elevatable to move a load carried on the lift of the truck and which is adjustable angularly with respect to vertical,

a column of racks having a plurality of compartments for receiving loads,

vertical guides at the respective sides of said column of racks,

a carriage engaging either the guides or the mast and engageable with the other thereof,

said carriage when engaged with the guides and mast being confined by the guides to vertical movement only as the mast is moved vertically, such engagement preventing motion of the carriage and mast with respect to the guides in any but a vertical direction.

13. The combination of claim 12 wherein the vertical guides comprise a pair of spaced tracks,

and wherein the carriage is connected to and between the tracks and includes a coupling for engagement by the mast of the lift, the carriage when so coupled to the mast limiting movement of the mast to vertical movement only.

14. The combination of claim 12 which further includes angulation indicator means showing the angulation of the mast of the lift truck with respect to vertical direction.

15. The combination of claim 12 which further includes stop means for arresting movement of the lift truck in the horizontal plane at a position such that the mast and carriage are in vertical alignment for engagement.

16. The combination'of claim 15 wherein the said i stop means includes a bumper mounted at the floor on 

1. A system for stabilizing the mast of a lift truck as the latter is moving a load vertically at a storage rack, comprising, fixed vertical guide means presented at a storage rack and extending vertically the distance over which mast stabilization is to be provided, a carriage which is translatable vertically along said guide means, an interconnection for coupling said carriage to said guide means for vertical travel with respect thereto, the interconnection of the carriage to the guide means confining the carriage to movement along a vertical path on the guide means and preventing movement of the carriage in a horizontal direction with respect to the said guide means, coupling means on said truck adjacent the top of said mast for connecting said mast to said carriage so that said carriage will be moved vertically along said guide means as said mast is moved vertically while said mast is connected to said carriage, and means for selectively disconnecting said carriage from one of the mast and the vertical guide means so that the truck can move to other racks.
 2. The system of claim 1 wherein the vertical guide means comprises two spaced vertical tracks, and wherein said carriage is mounted to and between said racks for vertical travel thereover.
 3. The system of claim 2 wherein the vertical guide means comprise two spaced I-beams mounted at the respective sides of a column of racks.
 4. The system of claim 3 wherein the said interconnection includes rollers on said carriage that track on flanges of said I-beams for rolling movement of the carriage with respect to the beams.
 5. The system of claim 1 wherein the said coupling means comprises an upstanding post on said mast, and a cooperating downwardly opening socket on said carriage.
 6. The system of claim 1 wherein the vertical guide means comprises vertical tracks, said carriage being fixed on said tracks by said interconnection for vertical travel therEover, and wherein an element projects from the mast and disconnectably interfits with the carriage.
 7. The system of claim 1 which further includes stop means for stopping the lift truck at a predetermined position in front of the rack, such that the carriage is in vertical alignment for connection to said one of the mast and the vertical guide means.
 8. The system of claim 1 which further includes a stop on the guide means which limits the extent of downward travel of the carriage on the guide means.
 9. The system of claim 1 wherein the guide means comprises a pair of vertical cables mounted adjacent the rack, said carriage comprises a cross member connected between the cables for vertical movement thereover, and wherein said interconnection comprises sleeves at the respective ends of said cross member slidable over said cables.
 10. The system of claim 1 which further includes an elevation indicator providing a readout at ground level of the elevation indicator providing a readout at ground level of the height of the load carried by the lift.
 11. The system of claim 10 wherein the elevation indicator comprises a flexible tape connected at one end to the carriage, said indicator including spring rewind means and a dial operated by the rewind means.
 12. In combination, a lift truck having a mast which is elevatable to move a load carried on the lift of the truck and which is adjustable angularly with respect to vertical, a column of racks having a plurality of compartments for receiving loads, vertical guides at the respective sides of said column of racks, a carriage engaging either the guides or the mast and engageable with the other thereof, said carriage when engaged with the guides and mast being confined by the guides to vertical movement only as the mast is moved vertically, such engagement preventing motion of the carriage and mast with respect to the guides in any but a vertical direction.
 13. The combination of claim 12 wherein the vertical guides comprise a pair of spaced tracks, and wherein the carriage is connected to and between the tracks and includes a coupling for engagement by the mast of the lift, the carriage when so coupled to the mast limiting movement of the mast to vertical movement only.
 14. The combination of claim 12 which further includes angulation indicator means showing the angulation of the mast of the lift truck with respect to vertical direction.
 15. The combination of claim 12 which further includes stop means for arresting movement of the lift truck in the horizontal plane at a position such that the mast and carriage are in vertical alignment for engagement.
 16. The combination of claim 15 wherein the said stop means includes a bumper mounted at the floor on which said track moves. 